1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus of a contact-type to develop an image using a single-component nonmagnetic toner.
2. Description of the Related Art
An example of a conventional image forming apparatus of a contact-type to develop an electrostatic latent image using a single-component nonmagnetic toner is schematically illustrated in FIG. 1.
Referring to FIG. 1, the image forming apparatus includes a photoconductive medium 1. The photoconductive medium 1 is rotatably mounted on a main body frame (not shown) of the image forming apparatus, and the electrostatic latent image is formed on a surface thereof by electrification and light exposure.
The image forming apparatus further includes a developing roller 2 which is rotatably mounted in a developing unit 3 to contact the photoconductive medium 1. The developing unit 3 includes a toner receptacle 3a where a toner is stored. In the developing unit 3, a toner supplying roller 4 is also rotatably mounted to supply the toner contained in the toner receptacle 3a to the developing roller 2.
The developing unit 3 further includes agitators 5 and 6 to agitate the toner stored in the toner receptacle 3a, and a toner controlling blade 7 to remove an excessive toner from the developing roller 2 to form a regularly thin film on a surface of the developing roller.
The electrostatic latent image formed on the photoconductive medium 1 is developed using the toner by the developing roller 2. The toner is supplied from the toner receptacle 3a to the developing roller 2 by the toner supplying roller 4, controlled by the toner controlling blade 7 to form the thin film, and then moved to the photoconductive medium 1.
The toner supplying roller 4 rotates in an opposite direction of a tangent line of the developing roller 2, that is, in a counterclockwise direction shown in FIG. 1, and supplies the toner to the developing roller 2 as described. The toner supplying roller 4 also collects a residual toner remaining on the developing roller 2 after the electrostatic latent image is developed, and a remaining electric potential of the developing roller 2 and/or the toner supplying roller 4 is reset.
The toner supplying roller 4 is usually shaped in a fur brush form. Therefore, especially in hot and damp environment, the toner is likely to be stagnant and impregnated under the toner supplying roller 4, thereby losing its fluidity due to heat and humidity.
When the toner becomes stagnant under the toner supplying roller 4, the toner is repeatedly stressed at a first nip defined between the developing roller 2 and the toner supplying roller 4, a second nip between the developing roller 2 and the toner controlling blade 7, and a third nip between the developing roller 2 and the photoconductive medium 1. Accordingly, there are problems causing deterioration of an image quality, i.e., a ‘background phenomenon’, since a toner electrifying capability and a toner collecting capability deteriorate, and the toner to be mixed with the toner stored in the toner receptacle 3a becomes harder.
Therefore, there is a need to maintain the toner electrifying capability and the toner collecting capability of the toner supplying roller 4.